Recently, a hybrid vehicle has been receiving attention as an environmentally friendly vehicle. The hybrid vehicle has, as power sources, a DC power supply, an inverter, and a motor driven by the inverter, in addition to a conventional engine. In other words, the hybrid vehicle obtains the power sources by driving the engine, and in addition, by converting a DC voltage from the DC power supply to an AC voltage through the use of the inverter and rotating the motor with the converted AC voltage.
As one type of such hybrid vehicle, Japanese Patent Laying-Open No. 2007-28733 (Patent Document 1), for example, discloses a so-called parallel hybrid vehicle. In the parallel hybrid vehicle, a part of motive power output from an engine is transmitted to a drive shaft through a power split device having a first motor generator, and the remaining motive power is regenerated as electric power by the first motor generator. This electric power is used to charge a battery or to drive a second motor generator serving as a power source other than the engine.
In such parallel hybrid vehicle, however, when an abnormality occurs in the engine or the first motor generator, the normal vehicle traveling in which the engine is used as a main power source becomes impossible. For this reason, Patent Document 1 discloses a technique of performing a limp-home operation using the second motor generator within the performance range determined in accordance with the charging amount of a secondary battery, when the engine or the first motor generator is abnormal, and thereby extending the distance traveled during the limp-home operation.
During such limp-home operation, the first motor generator rotates with the rotation of the second motor generator, because the first and second motor generators are coupled to the same output shaft. For this reason, when a short-circuit fault is occurring within an inverter connected to the first motor generator, a short-circuit current may be generated within the inverter during the limp-home operation, due to an induced voltage generated at the first motor generator.
Therefore, the vehicle in Patent Document 1 is configured to restrict the limp-home operation using the second motor generator when an excessive current flows through the inverter connected to the first motor generator during the limp-home operation. As a result, the occurrence of further damage to elements resulting from the generation of a high temperature exceeding the heat-resistant temperature of inverter components due to the excessive short-circuit current is prevented.    Patent Document 1: Japanese Patent Laying-Open No. 2007-28733    Patent Document 2: Japanese Patent Laying-Open No. 2006-170120    Patent Document 3: Japanese Patent Laying-Open No. 2007-245966    Patent Document 4: Japanese Patent Laying-Open No. 8-182105    Patent Document 5: Japanese Patent Laying-Open No. 2007-244126